The present invention relates to a method for controlling the brake system of a two-channel anti-lock system (two-channel ABS), wherein the wheel rotational behavior is measured and analyzed for generating a vehicle reference speed and braking-pressure control signals. Quantities determining the braking pressure in the wheel brakes are measured and from which measured quantities a wheel pressure pattern is derived that is by approximation representative of the pressure variation in the wheel brakes and, in conjunction with the wheel rotational behavior, is taken into account for the purpose of wheel slip control and/or for determining the braking-pressure control signals. A circuit configuration for implementing this method is provided.
In known electronic anti-lock systems, the information required for regulating the braking pressure is obtained by virtue of wheel sensors which generate for each monitored wheel an electric signal indicative of the wheel rotational behavior. As is conventional, the vehicle speed is defined by approximation by logically combining the wheel speed signals. In some braking situations or under specific conditions, for example, in the even of all-wheel drive, it is however difficult if not impossible to derive the vehicle speed sufficiently exactly from the wheel rotational behavior. For this reason, vehicle sensors measuring the translational speed, the translational acceleration or deceleration, braking pressure sensors or the like additionally have been mounted on vehicles.
However, for cost reasons, attempts are being made to utilize wheel sensors alone, and preferably only a small number of such sensors. Thus far, four wheel sensors, and under certain circumstances only three, have been considered to be necessary for a satisfactory control even in an anti-lock system with merely two control channels and, preferably, the pressure is regulated separately in each diagonal.
In principle, a control operation could be improved if the actual braking pressure that is prevailing when the control commences and/or when a wheel becomes unstable were known For this purpose, anti-lock systems are known which are additionally equipped with braking pressure sensors.
German patent application P38 09 100.3 suggests forming a wheel pressure pattern instead of measuring the actual braking pressure. Information on the pressure variation is approximately received by measuring, counting and integrating the pulses which serve to open and/or close the inlet valves and outlets valves, while additional consideration of the characteristic curves of braking-pressure increase and decrease of the wheel brakes is possible. The data relating to the instantaneous pressure obtained in this matter are taken into consideration when dimensioning the valve control pulses.
It is a general object of the present invention to more effectively analyze the information received by wheel sensors for the purpose of improving the control and/or reducing the expenditure of the sensors. It is a further object to devise a state-of-the-art two-channel anti-lock control while a minimum expenditure in the sensors.